Beam spot tuning in a radiation therapy system

ABSTRACT

An example computer-implemented method for tuning a beam spot in a radiation therapy system has been disclosed. The example method includes configuring an electron beam to generate a first beam spot on an electron-beam target of the radiation therapy system, generating, using an imager of the radiation therapy system, a first plurality of projection images of the first beam spot, wherein each of the projection images of the first beam spot is generated with a line of sight blocked between the imager and a different respective portion of the beam spot, based on the first plurality of projection images, determining a value for one or more beam spot quality metrics associated with the first beam spot, and based on the value, determining whether the first beam spot is outside a specified quality range.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is also related in subject matter to U.S. patentapplication Ser. No. 17/216,695, filed Mar. 30, 2021, which isincorporated herein by reference.

BACKGROUND

Unless otherwise indicated herein, the approaches described in thissection are not prior art to the claims in this application and are notadmitted to be prior art by inclusion in this section.

Radiation therapy is a localized treatment for a specific anatomicaltarget (a planning target volume, or PTV), such as a cancerous tumor.Ideally, radiation therapy is performed on the planning target volumethat spares the surrounding normal tissue from receiving doses abovespecified tolerances, thereby minimizing risk of damage to healthytissue. Prior to the delivery of radiation therapy, an imaging system istypically employed to provide a three-dimensional image of theanatomical target and surrounding area. From such imaging, the size andmass of the anatomical target can be estimated, a planning target volumedetermined, and an appropriate treatment plan generated using adedicated treatment planning system (TPS). The TPS has photon- andelectron-beam models that accurately represent the beams generated bythe radiation therapy delivery system.

Currently, the field of radiation oncology is moving to treating smallerplanning target volumes, for example via stereotactic radiosurgery (SRS)and stereotactic radiotherapy (SRT). Stereotactic radiosurgery andstereotactic radiation therapy are advanced forms of radiation therapythat involve delivery of a high radiation dose to a small focused regionof a patient's anatomy. Because of the high radiation dose and smalltarget volumes associated with these SRS treatments, high geometricaccuracy of the delivered treatment is required. This high geometricalaccuracy is required for both the predicted dose distribution providedby the beam model in the TPS and the delivered dose provided by theactual treatment delivery system.

SUMMARY

According to various embodiments, a computer-implemented procedureincludes a direct measurement of beam spot size, shape, and intensitydistribution in a radiation therapy system using an existing imagingpanel of the radiation therapy system, and modification of one or moreattributes of a beam spot based on such measurements. Specifically, asequence of radiation projection images (e.g., X-ray projection images)are acquired with the imaging panel while a treatment beam is generatedand a multi-leaf collimator is positioned to block a portion of the beamand rotated about the center axis of the beam. Based on the projectionimages, a two-dimensional (2D) image of the beam spot is reconstructed,which indicates the area, size, shape, location, and 2D intensitytopography of the beam spot. Additionally, by shaping a small radiationfield and using the existing imaging panel to measure the radiationfield penumbra and output factor of the treatment beam can bedetermined. The computer-implemented procedure further includesmodifying the size, shape, and/or location of the beam spot based on thereconstructed 2D beam spot image, so that the beam spot meets athreshold value for one or more predetermined quality metrics. In someembodiments, the beam spot can be modified by changing an existing valuefor a parameter of an electron-beam-generating component of the systemto a new value. Additional iterations of beam spot measurement andelectron-beam modifications can be performed until the beam spot meetssuch threshold values. Because each iteration can be performed in a fewminutes as part of an automated process, the computer-implementedprocedure of the embodiments can be employed as part of factory setup,an on-site quality-assurance tool, and/or as a periodic service tool.Thus, penumbra and/or output factor deviations and other issues createdby asymmetric beam spots or beams that do not meet the necessarygeometrical requirements can be prevented. Further, a radiation targetenergy density per unit beam area can be confirmed to be withinacceptable limits, thereby ensuring reliable target power levels andextended target life for a radiation therapy system.

According to various embodiments, a computer-implemented procedureincludes measurement of one or more attributes of a radiation fieldgenerated by a beam spot using an existing imaging panel of theradiation therapy system, and modification of one or more attributes ofthe beam spot based on such radiation field measurements. Attributes ofthe radiation field are quantified via one or more specific radiationfield quality metrics, which can indicate whether a radiation beamoriginating from the beam spot is outside a specified quality range.Examples of such radiation field quality metrics include one or more ofan area coincidence factor, a penumbra asymmetry factor, and a radiationbeam output factor.

The foregoing summary is illustrative only and is not intended to be inany way limiting. In addition to the illustrative aspects, embodiments,and features described above, further aspects, embodiments, and featureswill become apparent by reference to the drawings and the followingdetailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features of the present disclosure will becomemore fully apparent from the following description and appended claims,taken in conjunction with the accompanying drawings. These drawingsdepict only several embodiments in accordance with the disclosure andare, therefore, not to be considered limiting of its scope. Thedisclosure will be described with additional specificity and detailthrough use of the accompanying drawings.

FIG. 1 is a perspective view of a radiation therapy system that canbeneficially implement various aspects of the present disclosure.

FIG. 2 schematically illustrates a side view of the radiation therapysystem of FIG. 1 , according to various embodiments.

FIG. 3 schematically illustrates a treatment beam with an associatedtreatment beam penumbra for a particular beam limiting device.

FIG. 4 schematically illustrates a beam-generating subsystem of theradiation therapy system of FIG. 1 that can beneficially implementvarious embodiments.

FIG. 5 schematically illustrates a portion of a beam-generatingsubsystem of the radiation therapy system of FIG. 1 while a beam-spotimaging procedure is performed, according to various embodiments.

FIG. 6 schematically illustrates a beam spot image, according to variousembodiments.

FIG. 7 schematically illustrates various steps of an edge measurementalgorithm for generating a 2D image of a beam spot, according to variousembodiments.

FIG. 8 sets forth a flowchart of a computer-implemented process fortuning a beam spot in a radiation therapy system, according to one ormore embodiments.

FIG. 9 schematically illustrates an aperture 900 and imager 910 forgenerating slit-field images, according to various embodiments.

FIG. 10 schematically illustrates a slit-field X-ray image and anassociated penumbra and output factor, according to various embodiments.

FIG. 11A-11C schematically illustrate determination of an areacoincidence factor for a particular combination of a treatment beam,aperture, and aperture orientation, according to various embodiments.

FIG. 12 sets forth a flowchart of a computer-implemented process fortuning a beam spot in a radiation therapy system based on measurementsof a radiation field, according to one or more embodiments.

FIG. 13 is an illustration of computing device configured to performvarious embodiments of the present disclosure.

FIG. 14 is a block diagram of an illustrative embodiment of a computerprogram product for implementing a method for segmenting an image,according to one or more embodiments of the present disclosure.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof. In the drawings,similar symbols typically identify similar components, unless contextdictates otherwise. The illustrative embodiments described in thedetailed description, drawings, and claims are not meant to be limiting.Other embodiments may be utilized, and other changes may be made,without departing from the spirit or scope of the subject matterpresented here. It will be readily understood that the aspects of thedisclosure, as generally described herein, and illustrated in thefigures, can be arranged, substituted, combined, and designed in a widevariety of different configurations, all of which are explicitlycontemplated and make part of this disclosure.

INTRODUCTION

As noted above, for radiation treatments that involve a high radiationdose and/or a small target size, high geometric accuracy of thedelivered radiation treatment is required. Many factors can affect theaccuracy of a delivered radiation treatment, including the size, shape,and location of the beam spot, which is the area on a radiation targetthat is struck by an electron beam and generates the treatment radiationbeam, such as an X-ray beam or other radiation beam, inlinear-accelerator-based radiation therapy systems. For example, toachieve the high spatial accuracy required for certain image-guidedradiation therapy (IGRT) treatments, the IGRT imaging isocenter mustclosely coincide with the treatment beam isocenter, and this isocentercoincidence is influenced by the alignment of the beam spot with thecollimator rotation axis. In another example, percentage depth dosedistribution and beam profiles of very small diameter (1.5-5 mm)megavoltage (MV) radiosurgical beams have been shown to depend on thediameter of the beam spot. In a further example, controlling andminimizing dose fall-off at the edges of a treatment beam (i.e., the“penumbra”) is important for sparing organs at risk in radiationtherapy, and the size, shape, and symmetry of the beam spot all directlyaffect the size and shape of the penumbra. Moreover, the output factorof such small fields, which is also dependent on the beam spotcharacteristics, has to meet tight specifications. In light of theabove, accurate knowledge of the geometry of a beam spot in a radiationtherapy system is of high importance, particularly for treatmentsinvolving a smaller planning target volume (PTV) and/or a high radiationdose and/or a sharp dose fall-off.

Unfortunately, direct measurement of the beam spot in a radiationtherapy system can be difficult to implement. As a result, fitting aplanning target volume with a high, uniform dose while limiting theirradiation of neighboring healthy tissues can be difficult to achieve.Conventional techniques for measuring properties of the beam spot of aradiation therapy system are time-consuming to set up and perform, relyon measuring equipment that is external to the radiation therapy system,and/or provide incomplete information about the beam spot. For example,a spot camera positioned between the radiation source of n radiationtherapy system and an electronic portal imaging device (EPID) of theradiation therapy system allows only parallel radiation from theradiation source to reach the EPID. As a result, the EPID can generatean image of the beam spot that shows the size, shape, and position ofthe beam spot. However, a spot camera is a bulky piece of specializedequipment external to the radiation therapy system, requiring preciseand time-consuming setup and training to be used. In another example, aprobe external to a radiation therapy system can be employed inconjunction with a water tank to traverse the radiation field of theradiation source and generate profiles of radiation intensity across theradiation field. Such profiles can provide relative information aboutthe beam spot and penumbra symmetry. However, this approach alsoinvolves the time-consuming setup and manual operation of equipmentexternal to the radiation therapy system, greatly limiting where and howfrequently this approach can be employed. Further, the informationobtained does not indicate the actual size of the penumbra or theintensity distribution of the beam spot itself.

According to various embodiments, a computer-implemented procedureincludes a direct measurement of beam spot size, shape, location,orientation, and intensity distribution in a radiation therapy system,using an existing (“on-board”) imaging panel of the radiation therapysystem. Based on a sequence of projection images that are acquired withthe on-board imaging panel, a two-dimensional (2D) image of the beamspot is reconstructed, which indicates the area, size, shape, location,orientation, and 2D intensity topography of the beam spot, including theradiation penumbra and the output factor of the treatment beam.Radiation penumbra is a parameter describing the dose delivered and thefall-off of dose profiles in the patient, and in some embodiments isgiven by the difference between the projected distances of the 80% and20% dose values in a 2-dimensional projection of the dose distribution.For the small fields employed in SRS treatments, penumbra is highlydependent on the radiation beam spot size, shape, and location withrespect to the central axis of the collimator system of the radiationtherapy system. Additionally, the radiation output factor of the SRSfield is dependent on certain beam spot characteristics. Therefore,enforcing pre-determined quality metrics on the beam spot ensures thatboth the penumbra and output factors are tightly controlled and meettight tolerances mandated by the geometrical accuracy of SRS treatmentsand small field dosimetry. The beam spot and penumbra of a treatmentbeam in a radiation therapy system are described in greater detail belowin conjunction with FIGS. 3-5 .

In some embodiments, the computer-implemented procedure further includesmodifying the size, shape, and/or location of the beam spot and/orpenumbra based on the reconstructed 2D beam spot image, so that the beamspot meets a threshold value for one or more predetermined beam spotquality metrics. In some embodiments, such beam spot quality metricsinclude one or more of a beam spot area, a beam spot elongation, a beamspot power per unit area factor, and/or a beam spot center point offsetfrom an ideal center point location.

The herein-described embodiments facilitate tuning of a beam spot toachieve superior beam quality metrics and improve consistency betweenthe attributes of the beam spot and the overall beam tuning of thetreatment delivery system and pre-configured beam data that is includedin a treatment planning model of a TPS. Pre-configured beam data is aset of beam measurements (e.g., beam profiles, percent depth dose and/oroutput factors) acquired using a dedicated 3-dimensional water scanningsystem and radiation detectors. Generally, such pre-configured beam dataresides in the TPS that is used for treatment plan creation. As aresult, in the embodiments, performance of a radiation beam generated bythe beam spot closely matches the performance assumed for the radiationbeam in the TPS.

SYSTEM OVERVIEW

FIG. 1 is a perspective view of a radiation therapy system 100 that canbeneficially implement various aspects of the present disclosure.Radiation therapy (RT) system 100 is a radiation system may beconfigured to detect intra-fraction motion in near-real time using X-rayimaging techniques. Thus, in some embodiments, RT system 100 isconfigured to provide stereotactic radiosurgery and precisionradiotherapy for lesions, tumors, and conditions anywhere in the bodywhere radiation treatment is indicated. As such, RT system 100 caninclude one or more of a linear accelerator (LINAC) 104 that generatesan MV treatment beam of high energy X-rays or other radiation, one ormore kilovolt (kV) X-ray sources 106, one or more imaging panels 107(e.g., an X-ray imager), and an MV electronic portal imaging device(EPID) 105. By way of example, RT system 100 is described hereinconfigured with a C-arm gantry 110 capable of infinite rotation via aslip ring connection. In other embodiments, RT system 100 can beconfigured with a circular gantry mounted on a drive stand, or any othertechnically feasible configuration that enables radiation therapy andimaging of a PTV.

In some embodiments, RT system 100 is capable of X-ray imaging of atarget volume immediately prior to and/or during application of an MVtreatment beam, so that an IGRT and/or an intensity-modulated radiationtherapy (IMRT) process can be performed using X-ray imaging. Forexample, in some embodiments, RT system 100 includes kV imaging of a PTVin conjunction with imaging generated by the MV treatment beam. RTsystem 100 may include one or more touchscreens 101 for patientinformation verification, couch motion controls 102, a radiation area103, a base positioning assembly 112, a couch 108 disposed on basepositioning assembly 112, and an image acquisition and treatment controlcomputer 109, all of which are disposed within a treatment room. RTsystem 100 further includes a remote control console 111, which isdisposed outside the treatment room and enables treatment delivery andpatient monitoring from a remote location. In some embodiments, imageacquisition and treatment control computer 109 and/or remote controlconsole 111 is configured to execute a treatment planning system thatincludes photon-beam, electron-beam, and/or other treatment planningmodels that accurately represent the beams generated by RT system 100.Such models include pre-configured beam data that assumes specificattributes of the beam spot that generates a treatment beam. Basepositioning assembly 112 is configured to precisely position couch 108with respect to radiation area 103, and motion controls 102 includeinput devices, such as buttons and/or switches, that enable a user tooperate base positioning assembly 112 to automatically and preciselyposition couch 108 to a predetermined location with respect to radiationarea 103. Motion controls 102 also enable a user to manually positioncouch 108 to a predetermined location.

FIG. 2 schematically illustrates a side view of RT system 100, accordingto various embodiments. As shown, RT system 100 includes a base stand200 and C-arm gantry 110. In FIG. 2 , base positioning assembly 112,couch 108, and X-ray source 106 are omitted for clarity. Base stand 200is a fixed support structure for components of RT treatment system 100,including C-arm gantry 110 and a drive system (not shown) for rotatablymoving C-arm gantry 110 about a horizontal rotation axis 202. Base stand200 rests on and/or is fixed to a support surface that is external to RTtreatment system 100, such as a floor of an RT treatment facility. C-armgantry 110 is rotationally coupled to base stand 200 and is a supportstructure on which various components of RT system 100 are mounted,including LINAC 104, EPID 105, imaging X-ray source 106 (not shown inFIG. 2 ), and imaging panel 107. During operation of RT treatment system100, C-arm gantry 110 rotates about radiation area 103 when actuated bythe drive system.

Imaging X-ray source 106 is configured to direct a conical beam ofX-rays, referred to herein as imaging X-rays (not shown in FIG. 2 forclarity), through an isocenter 203 of RT system 100 to imaging panel107. Isocenter 203 typically corresponds to the location of a targetvolume 209 to be treated, such as a PTV. In the embodiment illustratedin FIG. 2 , imaging panel 107 is depicted as a planar device, whereas inother embodiments, imaging panel 107 can have a curved configuration. Inthe embodiment illustrated in FIGS. 1 and 2 , RT system 100 includes asingle imaging panel and a single corresponding imaging radiation sourcein addition to EPID 105. In other embodiments, RT system 100 can includetwo or more imaging panels, each with a corresponding imaging radiationsource.

LINAC 104 typically includes one or more of an electron gun forgenerating electrons, an accelerating waveguide, an electron beamtarget, an electron beam transport means (such as a bending magnet) fordirecting the electron beam to the electron beam target, and/or acollimator assembly 208 for collimating and shaping a treatment beam 230that originates from the electron beam target. Collimator assembly 208typically includes one or more of a primary collimator that defines thelargest available circular radiation field for treatment beam 230, asecondary collimator for providing a rectangular or square radiationfield at isocenter 203 (for example via X-jaws and Y-jaws), and amultileaf collimator (MLC) for conforming treatment beam 230 to a PTV orother target volume.

During radiation treatment, in some embodiments LINAC 104 is configuredto generate treatment beam 230, which can include high-energy radiation(for example MV X-rays or MV electrons). In other embodiments, treatmentbeam 230 includes electrons, protons, and/or other heavy chargedparticles, ultra-high dose rate X-rays (e.g., for FLASH radiotherapy),and/or microbeams for microbeam radiation therapy. In addition, imagingpanel 107 is configured to receive imaging radiation and generatesuitable projection images therefrom. Further, in some embodiments, astreatment beam 230 is directed to isocenter 203 while C-arm gantry 110rotates through a treatment arc, image acquisitions can be performed viaEPID 105 to generate image data for target volume 209. For example, insuch embodiments, EPID 105 generates one or more projection images oftarget volume 209 and/or a region of patient anatomy surrounding targetvolume 209. Thus, projection images (e.g., 2D X-ray images) of targetvolume 209 can be generated during portions of an IGRT or IMRT processvia imaging panel 107 and/or EPID 105. Such projection images can thenbe employed to construct or update portions of imaging data for adigital volume that corresponds to a three-dimensional (3D) region thatincludes target volume 209. That is, a 3D image of such a 3D region isreconstructed from the projection images. In some embodiments, cone-beamcomputed tomography (CBCT) and/or digital tomosynthesis (DTS) can beused to process the projection images generated by imaging panel 107.

As noted above, LINAC 104 is configured to generate treatment beam 230during radiation treatment. For radiation treatments that involve a highradiation dose and/or a small target size, such as stereotacticradiosurgery (SRS) and stereotactic radiotherapy (SRT), the requiredgeometric accuracy of the delivery of treatment beam 230 can beadversely affected by the size, shape, location, and/or asymmetry of thetreatment beam penumbra. A treatment beam penumbra is described below inconjunction with FIG. 3 .

FIG. 3 schematically illustrates treatment beam 230 with an associatedtreatment beam penumbra 301 for a particular beam-limiting device. Asshown, treatment beam 230 is generated by a beam spot 302(cross-hatched) on an electron beam target 303 that is located in atarget plane 304. Beam spot 302 is typically generated by an electronbeam (not shown) that is directed onto electron beam target 303 by anaccelerating waveguide and electron beam transport means (such as abending magnet) of LINAC 104. The electron beam creates beam spot 302 onelectron beam target 303 from which treatment beam 230 originates. Beamspot 302 has a 3D distribution, which can be quantified via a 2Dintensity distribution 305 that represents the electron beamdistribution striking electron-beam target 303. 2D intensitydistribution 305 is depicted as a one-dimensional function in FIG. 3 ,but in practice, 2D intensity distribution 305 of beam spot 302 variesover a 2D region of electron beam target 303.

Treatment beam 230 is shaped by one or more MLCs 306 of RT system 100,passes through isocenter 203 of RT therapy system 100, and strikes EPID105. Ideally, a center axis 307 of treatment beam 230 is aligned withisocenter 203 and with collimator rotation axis 308, about which MLC 306may rotate. However, even when beam spot 302 is positioned on electronbeam target 303 so that center axis 307 of treatment beam 230 is alignedwith collimator rotation axis 308 (as shown in FIG. 3 ), beam spot 302produces penumbra 301, which is a region at the edge of treatment beam230 in which there is significant dose fall-off. Penumbra 301 isgenerated because beam spot 302 is not a single point, but instead is a2D area on electron beam target 303.

In the instance illustrated in FIG. 3 , penumbra 301 is depicted as ageometric penumbra of treatment beam 230. In other instances, penumbra301, when referenced herein, can further include a transmission penumbraof treatment beam 230, which occurs when a portion of treatment beam 230passes through an edge of a collimator (e.g., a jaw and/or MLC) beforereaching the full attenuation point of the collimator. Thus, in someinstances, the term “penumbra” can refer to a geometric penumbra of atreatment beam, a transmission penumbra of a treatment beam, and/or atotal penumbra of a treatment beam, which is a combination of thegeometric penumbra and the transmission penumbra.

The dose fall-off in a radiation therapy system associated with penumbra301 can degrade the high spatial accuracy required for certain radiationtherapy treatments using treatment beam 230. As a result, radiationtherapy systems are typically configured to minimize or otherwise reducea width 309 of penumbra 301. Further, when beam spot 302 is asymmetricand/or off-center from collimator rotation axis 308 and/or isocenter203, width 309 generally varies at different portions of penumbra 301,which can complicate conforming treatment beam 230 to a PTV or othertarget volume. Consequently, precise and accurate knowledge of 2Dintensity distribution 305 of beam spot 302 in a radiation therapysystem can be highly beneficial, particularly for treatments involving asmall PTV and/or a high radiation dose. According to variousembodiments, such information regarding 2D intensity distribution 305can be determined using a conventional radiation therapy system.

FIG. 4 schematically illustrates a beam-generating subsystem 400 of RTsystem 100 that can beneficially implement various embodiments.Beam-generating subsystem 400 includes components of RT system 100 forgenerating treatment beam 230 and for generating X-ray projection imagesof beam spot 302 according to various embodiments. In the embodimentillustrated in FIG. 4 , beam-generating subsystem 400 includes LINAC104, collimator assembly 208, and EPID 105. LINAC 104 includes anelectron gun 401 for generating an electron beam 421, an acceleratingwaveguide 402 for accelerating the electrons of electron beam 421, afirst beam-shaping solenoid 411, a second beam-shaping solenoid 412,electron beam target 303, and/or an electron beam transport means (suchas a bending magnet) 403. While collimator assembly 208 may typicallyinclude one or more of a primary collimator, a secondary collimator, oneor more filters, an ionization chamber, MLC 306, and/or othercomponents, for clarity the only portion of collimator assembly 208shown in FIG. 4 is MLC 306, which is configured to rotate aboutcollimator rotation axis 308. According to various embodiments, acomputer-implemented procedure provides a direct measurement of beamspot size, shape, and intensity distribution in RT system 100 usingbeam-generating subsystem 400. One such embodiment is illustrated belowin conjunction with FIG. 5 .

Beam Spot Measurement and Analysis

FIG. 5 schematically illustrates a portion of beam-generating subsystem400 while a beam-spot imaging procedure is performed, according tovarious embodiments. In the embodiments, a direct beam-spot measurementis performed that enables quantification of the size, shape, andlocation of 2D intensity distribution 305 of beam spot 302. As shown, inthe embodiments, a portion 506 of MLC 306 is parked so that asignificant portion 530 (e.g., approximately half) of treatment beam 230is blocked from reaching EPID 105. A sequence of X-ray projection imagesare then acquired of beam spot 302 with EPID 105 while MLC 306 isrotated about collimator rotation axis 308. Based on the X-rayprojection images of the different portions of beam spot 302, an imageof beam spot 302 is reconstructed that indicates the size, shape, andlocation of 2D intensity distribution 305 of beam spot 302. In someembodiments, a reconstruction algorithm (described below in conjunctionwith FIG. 7 ) is employed that uses a parallel-beam computed tomography(CT) reconstruction technique to compute the image of beam spot 302.

To generate the sequence of X-ray projection images of beam spot 302,MLC 306 is positioned at a plurality of different rotational anglesabout collimator rotation axis 308, so that at each different rotationalangle, line of sight between beam spot 302 and a different portion ofthe radiation beam is blocked by portion 506. Further, at each differentrotational angle, an X-ray projection image of beam spot 302 isgenerated with LINAC 104. Thus, for each X-ray projection image, adifferent portion of beam spot 302 is partially or completely viewableby EPID 105. For example, with MLC 306 positioned as shown in FIG. 5 , afirst region 505A of EPID 105 does not have line of sight to any of beamspot 302, a second region 505B of EPID 105 has line of sight to aportion of beam spot 302, a third region 505C of EPID 105 has line ofsight to a different portion of beam spot 302, and a fourth region 505Dof EPID 105 does not have line of sight to any of beam spot 302. As MLC306 rotates about collimator rotation axis 308, third region 505C andfourth region 505D of EPID 105 have lines of sight to different portionsof beam spot 302. Consequently, unless beam spot 302 is perfectlysymmetric and precisely centered on collimator rotation axis 308, eachsuch X-ray projection image has a different intensity distribution ofreceived X-rays from beam spot 302. Based on the different intensitydistribution of each X-ray projection image of beam spot 302, a 2D imageof beam spot 302 can be reconstructed. One embodiment of a 2D image of abeam spot is described below in conjunction with FIG. 6 .

FIG. 6 schematically illustrates a beam spot image 600, according tovarious embodiments. Beam spot image 600 is an image of a beam spot of aradiation therapy system, such as beam spot 302 of FIG. 3 , and isgenerated using an imager of a conventional radiation therapy system,such as EPID 105 of RT system 100. In the embodiments, beam spot image600 is reconstructed based on the above-described sequence of projectionimages of the beam spot and a so-called “edge measurement” algorithm(described below in conjunction with FIG. 7 ).

As shown in FIG. 6 , beam spot image 600 includes a 2D intensitydistribution 650 (cross-hatching) of the beam spot depicted by beam spotimage 600, where denser cross-hatching indicates a higher intensity ofX-rays (or other radiation) being generated. Thus, beam spot image 600includes information indicating how X-ray radiation intensity varieswithin a beam spot of a radiation therapy system. In some embodiments,based on such information, one or more beam spot quality metrics aredetermined for a particular beam spot, including one or more of a beamspot area, a beam spot elongation, a beam spot power per unit areafactor, and/or a beam spot center point offset 610.

The beam spot area for a beam spot is a quantified measure of the sizeof a beam spot and is calculated based on an area of beam spot image600. In some embodiments, a beam spot area of a beam spot is calculatedusing all pixels (not shown) in beam spot image 600 that indicategreater than zero radiation intensity. Alternatively, in someembodiments, a beam spot area of a beam spot is calculated using thepixels in beam spot image 600 that indicate a radiation intensity thatis greater than a predetermined radiation intensity level. In suchembodiments, the predetermined radiation intensity level can be anabsolute intensity level or a normalized intensity level, such as apercentage of a peak radiation intensity level indicated in beam spotimage 600. For example, in one such embodiment, a beam spot area of abeam spot is calculated using the pixels in beam spot image 600 thatindicate a radiation intensity that is greater than 50% of the peakradiation intensity level of beam spot image 600.

The beam spot elongation for a beam spot is a quantified measure of theshape (e.g., roundness and/or symmetry) of a beam spot and is calculatedbased on attributes of the beam spot visible in beam spot image 600. Insome embodiments, a beam spot elongation of a beam spot is calculatedusing geometrical attributes of the beam spot that are detectable inbeam spot image 600, such as a length 601 of a major axis of the beamspot and a length 602 of a minor axis of the beam spot. In suchembodiments, the beam spot elongation is the ratio of length 601 andlength 602. In such embodiments, length 601 and length 602 may bedetermined for the entire beam spot visible in beam spot image 600.Alternatively, in such embodiments, length 601 and length 602 aredetermined for a higher-intensity portion of the beam spot visible inbeam spot image 600. For example, in the embodiment illustrated in FIG.6 , length 601 and length 602 are determined for the portion of the beamspot visible in beam spot image 600 that is equal to or greater than 40%of the peak radiation intensity level of beam spot image 600. Thus, insuch an embodiment, a lower-intensity portion of beam spot image 600 isignored in determining length 601 and length 602.

The beam spot power per unit area factor for a beam spot is a quantifiedmeasure of the concentration of X-ray-generating power present in aparticular beam spot. In some embodiments, the beam spot power per unitarea factor for a beam spot quantifies the highest power concentrationdetected for a particular beam spot. In some embodiments, the beam spotpower per unit area factor of a beam spot is calculated based on thebeam spot area and on information associated with the electron beamemployed to generate the beam spot. In such embodiments, the beam spotarea may be calculated as described above, for example using the pixelsin beam spot image 600 that indicate a radiation intensity that isgreater than a particular percentage of the peak radiation intensitylevel of beam spot image 600. In some embodiments, the beam spot powerper unit area factor of a beam spot is calculated as a ratio of a powervalue per unit area. In such embodiments, the power value can be basedon a peak power of the electron beam employed to generate the beam spot.Further, in such embodiments, the power value can be based on afrequency of the electron beam employed to generate the beam spot and apulse width of the electron beam employed to generate the beam spot.

Beam spot center point offset 610 is a measure of a distance a centerpoint 611 of a beam spot is located from an ideal center point location612 of the beam spot. In some embodiments, center point 611 isdetermined based on the entire beam spot visible in beam spot image 600.Alternatively, in some embodiments, center point 611 is determined basedon a higher-intensity portion of the beam spot visible in beam spotimage 600, such as the portion of the beam spot visible in beam spotimage 600 that is equal to or greater than 40% of the peak radiationintensity level of beam spot image 600. In some embodiments, idealcenter point location 612 of the beam spot corresponds to a collimatorrotation axis of RT system 100, such as collimator rotation axis 308 inFIG. 3 , about which MLC 306 rotates. Thus, in such embodiments, beamspot center point offset 610 may indicate how aligned a center axis of atreatment beam (e.g., center axis 307 in FIG. 3 of treatment beam 230)is with a collimator rotation axis (e.g., collimator rotation axis 308in FIG. 3 ). Alternatively, in such embodiments, beam spot center pointoffset 610 may indicate how aligned beam spot 302 is with a collimatorrotation axis or some ideal or optimal location on an electron beamtarget (e.g., electron beam target 303 in FIG. 3 ).

As noted above, beam spot image 600 can be reconstructed based on thedifferent intensity distribution of each of the sequence of X-rayprojection images generated of beam spot 302 as MLC 306 is rotated aboutcollimator rotation axis 308, as shown in FIG. 3 . In some embodiments,an edge measurement algorithm is employed to generate beam spot image600 of beam spot 302. In such embodiments, the resultant 2D image ofbeam spot 302 corresponds to a 2D beam spot intensity distribution onelectron beam target 303. It is noted that in each X-ray projectionimage of beam spot 302, the relative intensity of received X-rays at anylocation in the X-ray projection image depends on how much of beam spot302 was covered by MLC 506 during acquisition of that X-ray projectionimage. One such edge measurement algorithm is schematically illustratedin FIG. 7 .

FIG. 7 schematically illustrates various steps of an edge measurementalgorithm for generating a 2D image of beam spot 302, according tovarious embodiments. As shown, MLC 306 is rotated about collimatorrotation axis 308, and at each of a plurality of different rotationalangles 701, an X-ray projection image 702 of beam spot 302 is generatedwith LINAC 104. As part of the edge measurement algorithm, each X-rayprojection image 702 of beam spot 302 is rotated to be a rotated X-rayprojection image 704, so that an edge 703 formed by portion 506 in eachrotated X-ray projection image 704 is oriented in the same way, forexample from a top edge 711 of the rotated X-ray projection image 704 toa bottom edge 712 of the rotated X-ray projection image 704. Assumingisotropic radiative emission from every point on beam spot 302, theintensity distribution along any one horizontal row of a rotated X-rayprojection image 704 is directly related to the fraction of beam spot302 that was exposed when the corresponding X-ray projection image 702was acquired. After averaging over all rows of pixels in a particularrotated X-ray projection image 704, the resulting horizontal intensitydistribution is like that of an edge spread function (ESF) 705, one ofwhich is generated for each rotated X-ray projection image 704. A linespread function (LSF) 706 is then generated from each ESF 705 associatedwith a particular rotated X-ray projection image 704, where LSF 706 fora particular rotated X-ray projection image 704 is a derivative of theESF 705 for the particular rotated X-ray projection image 704. Thus, foreach rotated X-ray projection image 704 of beam spot 302, a differentLSF 706 is generated. A sinogram (not shown) is then constructed usingthe different LSFs 706. When LSFs 706 are available from a sufficientnumber of projection angles, the sinogram can be used to recover theoriginal 2D intensity distribution 305 of beam spot 302 as a beam spotimage 750. A more detailed description of an edge measurement algorithmis described in “Dual Edge Apparatus And Algorithm for Measurement ofX-Ray Beam Spot Parameters,” Jeung, et al., Med. Phys. 45 (11), November2018.

In some embodiments, one or more attributes of a beam spot in aradiation therapy system are controlled or otherwise modified based onthe 2D intensity distribution determined for the beam spot as describedabove. In such embodiments, one or more parameters for anelectron-beam-shaping component of the radiation system is modifiedbased on the 2D intensity distribution for the beam spot, so that thesize, shape, location, and/or intensity distribution of a beam spot istuned to meet a predetermined specification. One such embodiment isdescribed below in conjunction with FIG. 8 .

FIG. 8 sets forth a flowchart of a computer-implemented process 800 fortuning a beam spot in a radiation therapy system, according to one ormore embodiments. Computer-implemented process 800 can be performed as apart of factory setup of a radiation therapy system, as an on-sitequality-assurance tool for the radiation therapy system, and/or as aperiodic service tool for the radiation therapy system.

Computer-implemented process 800 may include one or more operations,functions, or actions as illustrated by one or more of blocks 810-860.Although the blocks are illustrated in a sequential order, these blocksmay be performed in parallel, and/or in a different order than thosedescribed herein. Also, the various blocks may be combined into fewerblocks, divided into additional blocks, and/or eliminated based upon thedesired implementation. Although computer-implemented process 800 isdescribed in conjunction with the X-ray imaging system described hereinas part of RT system 100 and FIGS. 1-5 , persons skilled in the art willunderstand that any suitably configured X-ray imaging system is withinthe scope of the present embodiments.

The control algorithms for the blocks of computer-implemented process800 may be performed by any suitable computing device or devices. Forexample, in some embodiments, some or all of the control algorithms forthe blocks of computer-implemented process 800 reside in imageacquisition and treatment control computer 109, remote control console111, a combination of both, or any other computing devicecommunicatively coupled to RT system 100. The control algorithms can beimplemented in whole or in part as software- or firmware-implementedlogic, and/or as hardware-implemented logic circuits.

In step 810, a suitable computing device causes optimization of aparticular treatment beam to be performed. In some embodiments, suchtreatment beam optimization includes confirming a maximum dose rate oftreatment beam 230 using conventional techniques known in the art. Inaddition, in some embodiments, such treatment beam optimization furtherincludes modifying one or more beam-generation parameters associatedwith the dose rate of treatment beam 230 for the particularconfiguration of treatment beam 230 until the particular treatment beam230 is confirmed to have a specified dose rate. In some embodiments, theone or more beam-generation parameters include electron gun current, RFpower, energy switch position, one or more bending magnet parameters,one or more gun driver parameters, and/or the like. In some embodiments,the maximum dose rate of treatment beam 230 includes a margin above amaximum specified dose rate that is used in practice. When treatmentbeam 230 is confirmed to provide a suitable maximum dose rate, theoptimization of treatment beam 230 is complete and computer-implementedprocess 800 proceeds to step 820.

In step 820, the computing device causes beam spot 302 of RT system 100to be measured, for example by the acquisition of a sequence of X-rayprojection images of beam spot 302 and the application of an edgemeasurement algorithm, as described above in conjunction with FIG. 5 .In some embodiments, the output of such an algorithm includes a 2Dintensity distribution 305 of beam spot 302. In some embodiments, theoutput of such an algorithm includes information indicating a locationof a beam spot center point 611, for example relative to an absoluteposition on electron beam target 303.

In step 830, the computing device determines a value for one or morebeam spot quality metrics for beam spot 302, based on the output of step820. In some embodiments, the one or more beam spot quality metricsinclude a beam spot area, a beam spot elongation, a beam spot power perunit area factor, and/or a beam spot center point offset from an idealcenter point location, among others.

In step 840, the computing device determines whether beam spot 302satisfies a predetermined beam spot quality specification. When thecomputing device determines that beam spot 302 satisfies thepredetermined beam spot quality specification, computer-implementedprocess 800 proceeds to step 860. When the computing device determinesthat beam spot 302 fails to satisfy the predetermined beam spot qualityspecification, computer-implemented process 800 proceeds to step 850.

In some embodiments, in step 840 the computing device determines whetherbeam spot 302 satisfies the predetermined beam spot qualityspecification based on one or more beam spot quality metrics. Forexample, in one such embodiment, the computing device determines whetherbeam spot 302 satisfies the predetermined beam spot qualityspecification based on an eccentricity of beam spot 302. In such anembodiment, when a value determined in step 830 for the eccentricity ofbeam spot 302 is less than a threshold eccentricity value (such as aspecified maximum acceptable eccentricity for beam spot 302), thecomputing device determines that beam spot 302 satisfies thepredetermined beam spot quality specification. In another example, in anembodiment, the computing device determines whether beam spot 302satisfies the predetermined beam spot quality specification based on asize (e.g., area) of eccentricity of beam spot 302. In such anembodiment, when a value determined in step 830 for the area of beamspot 302 is less than a threshold maximum value (such as a specifiedmaximum acceptable area for beam spot 302), and is greater than athreshold minimum value (such as a specified minimum acceptable area forbeam spot 302), the computing device determines that beam spot 302satisfies the predetermined beam spot quality specification. In yetanother example, in an embodiment, the computing device determineswhether beam spot 302 satisfies the predetermined beam spot qualityspecification based on a power per unit area of beam spot 302. In suchan embodiment, when a value determined in step 830 for the area of beamspot 302 is greater than a threshold maximum value (such as a specifiedmaximum acceptable power per unit area for beam spot 302), the computingdevice determines that beam spot 302 does not satisfy the predeterminedbeam spot quality specification.

In some embodiments, in step 840 the computing device determines whetherbeam spot 302 satisfies the predetermined beam spot qualityspecification based multiple beam spot quality metrics. For example, insome embodiments, when the value determined in step 830 for each of themultiple beam spot quality metrics satisfies a respective specifiedthreshold or thresholds, the computing device determines that beam spot302 satisfies the predetermined beam spot quality specification. In suchembodiments, failure of a single value determined in step 830 to satisfya respective specified threshold or thresholds indicates that beam spot302 fails to satisfy the predetermined beam spot quality specification.Alternatively, in some embodiments, failure of one or more valuesdetermined in step 830 to satisfy a respective specified threshold orthresholds may not indicate that beam spot 302 fails to satisfy thepredetermined beam spot quality specification. Instead, in suchembodiments, a weighting scheme for each beam spot quality metric may beemployed to quantify how well each particular beam spot quality metricis satisfied. In such embodiments, an overall quality score for beamspot 302 is determined that is based on such a weighting scheme asapplied to the multiple values determined in step 830. In suchembodiments, a particular beam spot 302 may have an overall qualityscore indicating that the particular beam spot 302 satisfies thepredetermined beam spot quality specification even though a value forone or more beam spot quality metrics determined in step 830 may notsatisfy an associated threshold value for each of the one or more beamspot quality metrics. Further, in such embodiments, each beam spotquality metric may have a different score weighting, depending on therelative importance of each beam spot quality metric.

In some embodiments, a predetermined beam spot quality specification mayinclude multiple threshold values for one or more beam spot qualitymetrics for beam spot 302. In such embodiments, for a particular beamspot quality metric, the predetermined beam spot quality specificationmay include an upper threshold value and a lower threshold value forbeam spot 302. In such embodiments, the lower threshold value for aparticular beam spot quality metric may indicate an ideal threshold thatbeam spot 302 may, but is not required to, satisfy. By contrast, theupper threshold value for the particular beam spot quality metric mayindicate an undesired value at which beam spot 302 fails to satisfy thepredetermined beam spot quality specification, regardless of the overallquality score for beam spot 302 with respect to other beam qualitymetrics. That is, in such embodiments, failure of beam spot 302 tosatisfy the upper threshold indicates that the beam spot is not suitablefor use and should be modified. Alternatively, in some embodiments, theupper threshold value for a particular beam spot quality metricindicates a value at which beam spot 302 accrues a more severe scoringpenalty (higher scoring penalty or lower reward) than that associatedwith the lower threshold value for that particular beam spot qualitymetric. Alternatively, in some embodiments, the above-described roles ofthe upper threshold value and the lower threshold value for a particularbeam spot quality metric are reversed, i.e., the upper threshold valuefor a particular beam spot quality metric indicate an ideal thresholdvalue and the lower threshold value for the particular beam spot qualitymetric beam spot 302 indicates an undesired (or more heavily penalized)threshold value for the particular beam spot quality metric. Forexample, in the case of an area coincidence factor (described below inconjunction with FIGS. 10A-10C), a lower threshold value may indicate anundesired value for a beam spot.

In step 850, the computing device modifies one or more parameters of anelectron-beam-shaping component of RT system 100 to a new value. As aresult, one or more attributes of beam spot 302 are changed that affect2D intensity distribution 305 of beam spot 302, such as an eccentricityof beam spot 302, an average diameter of beam spot 302, an offsetdistance of beam spot 302, a size or area of beam spot 302, a power perunit area of beam spot 302, and/or the like. In some embodiments, theone or more parameters modified in step 850 are selected based on whichof the one or more beam spot quality metrics of the predetermined beamspot quality specification beam spot 302 failed to satisfy in step 840.Upon completion of step 850, computer-implemented process 800 returns tostep 820 and the computing device causes beam spot 302 of RT system 100to be measured again.

Examples of parameters of an electron-beam-shaping component of RTsystem 100 include a solenoid current for first beam-shaping solenoid411, a solenoid current for second beam-shaping solenoid 412, adirection of current flow in first beam-shaping solenoid 411, adirection of current flow in second beam-shaping solenoid 412, and/orthe like. Because the direction and magnitude of current flowing throughfirst beam-shaping solenoid 411 and second beam-shaping solenoid 412 canaffect the electron beam that generates beam spot 302 (and thereforetreatment beam 230), modification of such parameters also alters one ormore attributes of beam spot 302. Alternatively or additionally, in someembodiments, parameters of other beam-shaping components of RT system100 are modified in step 850 to alter one or more attributes of beamspot 302. Examples of other beam-shaping components of RT system 100include electron gun 401, accelerating waveguide 402, and/or electronbeam transport means 403.

In step 860, the computing device confirms that the maximum dose rate oftreatment beam 230 continues to have a specified maximum dose rate. Ininstances in which the maximum dose rate of treatment beam is below thespecified maximum dose rate, one or more beam-generation parametersassociated with the dose rate of treatment beam 230 are modified untiltreatment beam 230 is confirmed to have a specified dose rate. Uponcompletion of step 860, computer-implemented process 800 ends.

In some embodiments, steps 820-850 are performed over multipleiterations until specified attributes of treatment beam 230 satisfy apredetermined beam spot quality specification. Because each suchiteration can be completed in an automated fashion in a relatively shorttime (e.g., 1-5 minutes) and without the use of equipment and/ormeasuring instruments external to RT system 100, a particular treatmentbeam 230 can be tuned in a short time, for example in a fraction of anhour. Further, computer-implemented process 800 can be performed foreach of a plurality of treatment beam energies that may be employed byRT system 100. Because computer-implemented process 800 can be completedso quickly, computer-implemented process 800 can be performed as a partof factory setup of a radiation therapy system, as an on-sitequality-assurance tool for the radiation therapy system, and/or as aperiodic service tool for the radiation therapy system.

Implementation of computer-implemented process 800 enables precisecontrol of beam spot shape and size in RT system 100, thereby ensuringconsistency in a pre-configured treatment beam 230. Thus, treatment beam230 can meet tight the geometric tolerances and small field penumbrarequired for forms of radiation therapy that involve delivery of a highradiation dose to a small focused region of a patient's anatomy.Further, treatment beam 230 can be assumed to have substantially thesame attributes of the ideal treatment beam employed in treatmentplanning models.

Radiation Field Measurement and Analysis

In the embodiments described above, direct measurement of a beam spotenables tuning of one or more attributes of the beam spot in a radiationtherapy system. For example, based on such beam spot measurements, oneor more beam-shaping parameters that affect generation of the beam spotare modified so that the one or more attributes of the beam spot arechanged. In other embodiments, measurement of one or more attributes ofa radiation field generated by a beam spot enables similar tuning of thebeam spot. In such embodiments, one or more beam-shaping parameters aremodified based on the measured attributes of the radiation field, sothat the one or more attributes of the beam spot are changed. Theattributes of the radiation field are quantified via one or morespecific radiation field quality metrics that indicate whether aradiation beam originating from the beam spot is outside a specifiedquality range. Examples of such radiation field quality metrics includeone or more of an area coincidence factor, a penumbra asymmetry factor,and a beam output factor.

In some embodiments, values for one or more radiation field qualitymetrics are measured based on images that are generated using anexisting imaging panel of the radiation therapy system, such as EPID 105of RT system 100. In such embodiments, one or more slit-field images areemployed, in which a treatment beam (e.g., treatment beam 230 in FIG. 2) originating from a beam spot (e.g., beam spot 302 in FIG. 3 ) isshaped via a narrow rectangular aperture and imaged by EPID 105. Forexample, the narrow rectangular aperture can be formed by an MLC of theradiation therapy system, such as MLC 306 of RT system 100. As the MLCis rotated about a rotational axis, a different slit-field image isgenerated with the MLC at a different rotational orientation relative tothe imaging panel. Quantitative analysis of the different slit-fieldimages, as described herein, enables determination of the symmetry of aradiation field generated by a particular beam spot. One embodiment ofan aperture for generating slit-field images is described below inconjunction with FIG. 9 , and one embodiment of a slit-field image isdescribed below in conjunction with FIG. 10 .

FIG. 9 schematically illustrates an aperture 900 and imager 910 forgenerating slit-field images, according to various embodiments. In theembodiment illustrated in FIG. 9 , aperture 910 is formed by an MLC of aradiation therapy system, such as MLC 306 in FIG. 3 , and imager 910 isan imager included in the radiation therapy system, such as EPID 105 ofRT system 100. Aperture 900 and imager 910 are shown in a “beam's-eye”view in FIG. 9 , which is from the perspective of a source of atreatment beam, such as LINCAC 104 of RT system 100.

In the embodiment illustrated in FIG. 9 , multiple additionalorientations of aperture 900 with respect to imager 910 are shown thatcan each be employed to generate a slit-field image. The additionalorientations include an orientation 901, in which the MLC is positionedat a rotational angle of 45° about an axis of rotation 950 of thecollimator, an orientation 902, in which the MLC is positioned at arotational angle of 90° about axis of rotation 950, and an orientation903, in which the MLC is positioned at a rotational angle of 135° aboutthe axis of rotation 950. In other embodiments, more or fewerorientations of aperture 900 may be employed to generate slit-fieldimages.

FIG. 10 schematically illustrates a slit-field X-ray image 1000 and anassociated penumbra and output factor, according to various embodiments.Slit-field X-ray image 1000 is an X-ray image generated using atreatment beam, an imager, and an MLC of a conventional radiationtherapy system, such as treatment beam 230, EPID 105, and MLC 306 of RTsystem 100. In some embodiments, slit-field image 1000 is generated withEPID 105 positioned at or near isocenter 203 of RT system 100 ratherthan at a position employed during radiation treatment. In suchembodiments, the added complication of treatment beam 230 and theassociated penumbra being magnified is avoided.

As shown in FIG. 10 , slit-field X-ray image 1000 includes a 2Dintensity distribution 1050 of the radiation intensity, depicted bycross-hatching, where denser cross-hatching indicates a higher intensityof X-rays being received by EPID 105. Thus, slit-field X-ray image 1000includes information indicating how X-ray radiation intensity varieswithin a particular treatment beam 230, such as a treatment beam thathas a beam size similar to the width of the rectangular apertureemployed to generate slit-field X-ray image 1000. In some embodiments,based on such information, one or more radiation field quality metricsare determined for a particular beam spot and aperture combination,including one or more of an area coincidence factor, a penumbraasymmetry factor, and an X-ray beam output factor. In the embodiments,values for the one or more radiation field quality metrics are comparedto corresponding values of a predetermined radiation field qualityspecification to determine whether a treatment beam that generatesslit-field X-ray image 1000 is outside a specified quality range.

FIG. 10 further includes a one-dimensional X-ray intensity profile 1060that depicts X-ray dose along a linear portion 1061 of slit-field X-rayimage 1000. Thus, X-ray intensity profile 1060 indicates how radiationintensity varies across 2D intensity distribution 1050 of slit-fieldX-ray image 1000. In some embodiments, linear portion 1061 is orientedalong a major axis of slit-field X-ray image 1000. That is, linearportion 1061 is oriented parallel to the rectangular aperture employedto generate slit-field X-ray image 1000. Alternatively or additionally,a one-dimensional X-ray intensity profile can be generated for otherlinear portions of slit-field X-ray image 1000, such as along a minoraxis 1062 (which is perpendicular to the rectangular aperture employedto generate slit-field X-ray image 1000). Further, in the embodimentillustrated in FIG. 10 , X-ray intensity profile 1060 is normalized to apeak X-ray intensity value 1069 of one-dimensional X-ray intensityprofile 1060. Various radiation field quality metrics (area coincidencefactor, penumbra asymmetry factor, and X-ray beam output factor) are nowdescribed with respect to slit-field X-ray image 1000.

The penumbra asymmetry factor is a quantified measure of the symmetry ofthe penumbra of an X-ray beam, such as an X-ray beam used to generateslit-field X-ray image 1000. In some embodiments, the penumbra asymmetryfactor for an X-ray beam is based on a difference between a firstpenumbra portion 1063 of one-dimensional X-ray intensity profile 1060and a second penumbra portion 1064 of one-dimensional X-ray intensityprofile 1060. In such embodiments, first penumbra portion 1063 isdisposed on a first side of one-dimensional X-ray intensity profile1060, and second penumbra portion 1064 is disposed on a second side ofone-dimensional X-ray intensity profile 1060, where the first side isopposite the second side as shown in FIG. 10 .

In the embodiment illustrated in FIG. 10 , first penumbra portion 1063is defined as a width between a location 1065 of a radiation intensitythat corresponds to a beginning of a penumbra fall-off region on thefirst side of one-dimensional X-ray intensity profile 1060 and alocation 1066 of a radiation intensity that corresponds to an ending ofthe penumbra fall-off region on the first side of one-dimensional X-rayintensity profile 1060. Similarly, second penumbra portion 1064 isdefined as a width between a location 1067 of the radiation intensitythat corresponds to the beginning of the penumbra fall-off region on thesecond side of one-dimensional X-ray intensity profile 1060 and alocation 1068 of the radiation intensity that corresponds to the endingof the penumbra fall-off region on the second side of one-dimensionalX-ray intensity profile 1060. For example, in the embodiment illustratedin FIG. 10 , the radiation intensity that corresponds to the beginningof the penumbra fall-off region (locations 1065 and 1067) is 80% of peakradiation intensity level 1069 of one-dimensional X-ray intensityprofile 1060, and the radiation intensity that corresponds to the endingof the penumbra fall-off region (locations 1066 and 1068) is 20% of peakradiation intensity level 1069. In other embodiments, the radiationintensities that correspond to the beginning and ending of the penumbrafall-off region can vary from those shown in FIG. 10 .

The X-ray beam output factor is a quantified measure of the radiationintensity associated with the X-ray beam that generates slit-field X-rayimage 1000 relative to a reference X-ray beam. In some embodiments, theX-ray beam output factor is a ratio of the radiation intensityassociated with the X-ray beam of interest and the reference X-ray beam.Generally, the reference X-ray beam has a larger field than the X-raybeam that generates slit-field X-ray image 1000. For example, in anembodiment, the X-ray beam that generates slit-field X-ray image 1000has a field size of about 4 mm×7.5 mm, and the reference X-ray beam hasa field size of about 10 cm×10 cm. As a result, the X-ray beam outputfactor for an X-ray beam that generates slit-field X-ray image 1000 isgenerally less than 1. In some embodiments, for a specific combinationof rectangular aperture and treatment beam 230 that generates slit-fieldX-ray image 1000, the X-ray beam output factor is calculated formultiple orientations of the rectangular aperture (e.g., 0°, 45°, 90°,and 135°) around the beam collimator axis.

The area coincidence factor is a quantified measure of the variation inshape of a dose cloud of the X-ray beam that generates slit-field X-rayimage 1000. The dose cloud is the geometrical enclosure of points with adose larger or equal to a predefined intensity (e.g. an 80% isodosecontour). Specifically, the area coincidence factor quantifies thevariation in shape of such a dose cloud as the rectangular aperture thatforms the X-ray beam rotates through different angles. Thus, in someembodiments, for a particular treatment beam 230 and rectangularaperture, multiple values for the area coincidence factor aredetermined. For example, in one such embodiment, for the particulartreatment beam 230 and rectangular aperture, a different value for thearea coincidence factor is determined for each of multiple orientationsof the rectangular aperture (e.g., 0°, 45°, 90°, and 135°). One suchembodiment is described below in conjunction with FIGS. 11A-11C.

FIGS. 11A-11C schematically illustrate determination of an areacoincidence factor for a particular combination of treatment beam 230,rectangular aperture, and aperture orientation, according to variousembodiments. FIG. 11A illustrates a first step in a process ofgenerating the area coincident factor for the particular combination oftreatment beam 230 and rectangular aperture; FIG. 11B illustrates asecond step in the process of generating the area coincident factor; andFIG. 11C illustrates a third step in the process of generating the areacoincident factor.

FIG. 11A shows a reference dose cloud 1110 and an evaluated dose cloud1120 after acquisition of slit-field X-ray images 900 using theparticular combination of treatment beam 230 and rectangular aperture.In the embodiment illustrated in FIG. 11A, reference dose cloud 1110 isbased on a reference slit-field X-ray image (not shown) generated withthe rectangular aperture oriented at 0°, and evaluated dose cloud 1120is based on an evaluated slit-field X-ray image (not shown) generatedwith the rectangular aperture oriented at 45°. Further, in theembodiment illustrated in FIG. 11A, reference dose cloud 1110corresponds to a portion of the reference slit-field X-ray image thatrepresents a radiation intensity of 60% or more of a peak radiationintensity of the reference slit-field X-ray image. Thus, reference dosecloud 1110 does not include portions of the reference slit-field X-rayimage that indicate a radiation intensity of less than 60% of the peakradiation intensity of the reference slit-field X-ray image. Likewise,in FIG. 11A, evaluated dose cloud 1120 corresponds to a portion of theevaluated slit-field X-ray image that represents a radiation intensityof 60% or more of a peak radiation intensity of the evaluated slit-fieldX-ray image. Thus, evaluated dose cloud 1120 does not include portionsof the evaluated slit-field X-ray image that indicate a radiationintensity of less than 60% of the peak radiation intensity of theevaluated slit-field X-ray image. In other embodiments, reference dosecloud 1110 and evaluated dose cloud 1120 are defined based on a higheror lower radiation intensity cut-off than the 60% level illustrated inFIGS. 11A— 11C (e.g., 80% of a peak radiation intensity, 50% of a peakradiation intensity, etc.).

FIG. 11B shows evaluated dose cloud 1120 after being rotated to alignwith reference dose cloud 1110. Thus, in the embodiment illustrated inFIG. 11B, evaluated dose cloud 1120 is rotated 45° as shown, sinceevaluated dose cloud 1120 is based on an evaluated slit-field X-rayimage generated with the rectangular aperture oriented at 45°. In suchembodiments, the area coincidence factor determined for evaluated dosecloud 1120 enables variation in the shape of evaluated dose cloud 1120from reference dose cloud 1110 to be captured, as shown in FIG. 11C.

In addition, in some embodiments, to align evaluated dose cloud 1120with reference dose cloud 1110, evaluated dose cloud 1120 is rotatedabout a beam center point 1101, which corresponds to an ideal centerpoint of a treatment beam. For example, in some embodiments, beam centerpoint 1101 corresponds to a collimator rotation axis (such as collimatorrotation axis 308 in FIG. 3 ). Alternatively, beam center point 1101corresponds to some other absolute position on the imager that generatesthe reference slit-field X-ray image and the evaluated slit-field X-rayimage (e.g., EPID 105 of FIG. 2 ). In such embodiments, beam centerpoint 1101 does not necessarily correspond to a center point (such asthe centroid) of reference dose cloud 1110 or of evaluated dose cloud1120. In such embodiments, the area coincidence factor determined forevaluated dose cloud 1120 captures the difference in the position ofevaluated dose cloud 1120 (e.g., relative to beam center point 1101)from the position of reference dose cloud 1110. That is, when evaluateddose cloud 1120 is offset a different distance from beam center point1101 than reference dose cloud 1110, the area coincidence factorquantitatively captures the resulting reduction in coincidence(illustrated in FIG. 11C) between evaluated dose cloud 1120 andreference dose cloud 1110.

FIG. 11C shows evaluated dose cloud 1120 after being superimposed ontoreference dose cloud 1110. In some embodiments, evaluated dose cloud1120 is superimposed onto reference dose cloud 1110 based on thelocation of beam center point 1101 in reference dose cloud 1110 and inevaluated dose cloud 1120. In FIG. 11C, an area of coincidence 1102(cross-hatching) indicates a portion of evaluated dose cloud 1120 thatcoincides with reference dose cloud 1110. It is noted that differencesin shape and in position relative to beam center point 1101 can bothcontribute to a smaller area of coincidence 1102 between reference dosecloud 1110 and evaluated dose cloud 1120. In some embodiments, a valueof the area coincidence factor determined for a particular evaluateddose cloud 1120 is a normalized value based on area of coincidence 1102and a total area of either reference dose cloud 1110 or evaluated dosecloud 1120. Thus, in such embodiments, the value of the area coincidencefactor determined for a particular evaluated dose cloud 1120 isgenerally between 0 and 1.

FIG. 12 sets forth a flowchart of a computer-implemented process 1200for tuning a beam spot in a radiation therapy system based onmeasurements of a radiation field, according to one or more embodiments.In the embodiments, as part of the beam-tuning process, one or more ofthe above-described radiation field quality metrics are employed todetermine whether a beam spot is outside a specified quality range.Computer-implemented process 1200 can be performed as a part of factorysetup of a radiation therapy system, as an on-site quality-assurancetool for the radiation therapy system, and/or as a periodic service toolfor the radiation therapy system.

Computer-implemented process 1200 may include one or more operations,functions, or actions as illustrated by one or more of blocks 1210-1295.Although the blocks are illustrated in a sequential order, these blocksmay be performed in parallel, and/or in a different order than thosedescribed herein. Also, the various blocks may be combined into fewerblocks, divided into additional blocks, and/or eliminated based upon thedesired implementation. Although computer-implemented process 1200 isdescribed in conjunction with the X-ray imaging system described hereinas part of RT system 100 and FIGS. 1-5 , persons skilled in the art willunderstand that any suitably configured X-ray imaging system is withinthe scope of the present embodiments.

The control algorithms for the blocks of computer-implemented process1200 may be performed by any suitable computing device or devices. Forexample, in some embodiments, some or all of the control algorithms forthe blocks of computer-implemented process 1200 reside in imageacquisition and treatment control computer 109, remote control console111, a combination of both, or any other computing devicecommunicatively coupled to RT system 100. The control algorithms can beimplemented in whole or in part as software- or firmware-implementedlogic, and/or as hardware-implemented logic circuits.

In step 1210, a suitable computing device causes optimization of aparticular treatment beam to be performed. In some embodiments, suchtreatment beam optimization in includes confirming a maximum dose rateof treatment beam 230 using conventional techniques known in the artand, when required, performing one or more beam output optimizationprocedures configure treatment beam 230 to have a suitable maximum doserate. In some embodiments, step 1210 is substantially similar to step810 in computer-implemented process 800 of FIG. 8 .

In step 1215, one or more procedures are performed to ensure thattreatment beam 230 is correctly aligned with respect to collimatorrotation axis 308, about which MLC 306 rotates. Additionally, in someembodiments, one or more procedures are performed to ensure that afilter included in collimator assembly 208 is positioned correctly withrespect to collimator rotation axis 308. In some embodiments, tocomplete step 1215, conventional procedures known in the art may beperformed.

In step 1220, the computing device causes beam spot 302 of RT system 100to be measured, for example by the acquisition of a sequence of X-rayprojection images of beam spot 302 and the application of an edgemeasurement algorithm, as described above in conjunction with FIG. 5 .In some embodiments, step 1220 is substantially similar to step 820 incomputer-implemented process 800 of FIG. 8 .

In step 1230, the computing device determines a value for one or morebeam spot quality metrics for beam spot 302, based on the output of step1220. In some embodiments, step 1230 is substantially similar to step830 in computer-implemented process 800 of FIG. 8 .

In step 1240, the computing device determines whether beam spot 302satisfies a predetermined beam spot quality specification. When thecomputing device determines that beam spot 302 satisfies thepredetermined beam spot quality specification, computer-implementedprocess 1200 proceeds to step 1260. When the computing device determinesthat beam spot 302 fails to satisfy the predetermined beam spot qualityspecification, computer-implemented process 1200 proceeds to step 1250.In some embodiments, step 1240 is substantially similar to step 840 incomputer-implemented process 800 of FIG. 8 .

In step 1250, the computing device modifies one or more parameters of anelectron-beam-shaping component of RT system 100 to a new value. In someembodiments, step 1250 is substantially similar to step 850 incomputer-implemented process 800 of FIG. 8 .

In step 1260, the computing device causes one or more attributes of aradiation field generated by beam spot 302 to be measured. In someembodiments, in step 1260 one or more slit-field X-ray images of aradiation field of a treatment beam 230 are generated using EPID 105. Insuch embodiments, multiple slit-field X-ray images of the radiationfield may be generated, one slit-field X-ray image for each of multipleevaluation angles. In such embodiments, for each slit-field X-ray image,a rectangular aperture formed by MLC 306 is oriented at a differentevaluation angle.

In step 1265, the computing device radiation field analysis isperformed. In such embodiments, one or more radiation field qualitymetrics are determined, such as an area coincidence factor, a penumbraasymmetry factor, and/or an X-ray beam output factor.

In step 1270, the computing device determines whether a radiation fieldof treatment beam 230 (which was used to generate the multipleslit-field X-ray images) satisfies a predetermined radiation fieldquality specification. When the computing device determines that theradiation field satisfies the predetermined radiation field qualityspecification, computer-implemented process 1200 proceeds to step 1295.When the computing device determines that the radiation field fails tosatisfy the predetermined radiation field quality specification,computer-implemented process 1200 proceeds to step 1275.

In some embodiments, in step 1270 the computing device determineswhether the radiation field satisfies the predetermined radiation fieldquality specification based on one or more of the radiation fieldquality metrics determined in step 1265. In some embodiments, in step1270 the computing device determines whether the radiation fieldsatisfies the predetermined radiation field quality specification baseda scoring of multiple radiation field quality metrics. For example, insome embodiments, the radiation field fails to satisfy the predeterminedradiation field quality specification when a total score associated withthe radiation field does not meet or exceed a specified threshold valuefor the total score. Alternatively or additionally, in some embodiments,the radiation field fails to satisfy the predetermined radiation fieldquality specification when a value for at least one of the radiationfield quality metrics associated with the radiation field fails to meeta minimum required threshold value or exceeds a maximum allowablethreshold value for that radiation field quality metric. In someembodiments, each radiation field quality metric may have a differentscore weighting, depending on the relative importance of each radiationfield quality metric.

Further, in some embodiments, a predetermined radiation field qualityspecification may include multiple threshold values for one or moreradiation field quality metrics. Similar to the above-described beamspot quality metrics, in such embodiments, for a particular radiationfield quality metric, the predetermined radiation field qualityspecification may include one or more upper control limits and one ormore lower control limits for beam spot 302. In such embodiments, theupper and lower control limit values can indicate different scoringpenalties/rewards.

In step 1275, the computing device modifies one or more parameters of anelectron-beam-shaping component of RT system 100 to a new value. As aresult, one or more attributes of beam spot 302 are changed that affect2D intensity distribution 305 of beam spot 302 and, in turn, theradiation field of the treatment beam 230 generated by beam spot 302. Insome embodiments, step 1275 is substantially similar to step 1250described above.

In step 1280, the computing device causes optimization of the particulartreatment beam to be performed. In some embodiments, the computingdevice confirms a maximum dose rate of treatment beam 230 usingconventional techniques known in the art and, when required, performsone or more beam output optimization procedures configure treatment beam230 to have a suitable maximum dose rate. In some embodiments, step 1280is substantially similar to step 1210 described above.

In step 1285, one or more procedures are performed to ensure thattreatment beam 230 is correctly aligned with respect to collimatorrotation axis 308, about which MLC 306 rotates. In some embodiments,step 1285 is substantially similar to step 1215 described above.

In step 1290, the computing device causes optimization of the particulartreatment beam to be performed. In some embodiments, the computingdevice confirms a maximum dose rate of treatment beam 230 usingconventional techniques known in the art and, when required, performsone or more beam output optimization procedures configure treatment beam230 to have a suitable maximum dose rate. In some embodiments, step 1290is substantially similar to step 1210 described above. Upon completionof step 1290, computer-implemented process 1200 returns to step 1220.

In step 1295, computer-implemented process 1200 ends.

In the embodiments described above, the examples of slit-field imagesdepicted are generated using collimator aperture sizes associated with asmall-field radiation treatment (e.g., treatments involving radiationfields on the order of a few millimeters). In other embodiments,slit-field images that are generated for measuring the herein-describedradiation field quality metrics may be generated using differentcollimator apertures sizes, such as apertures associated with beam sizeson the order of one or more centimeters.

FIG. 13 is an illustration of a computing device 1300 configured toperform various embodiments of the present disclosure. Computing device1300 may be a desktop computer, a laptop computer, a smart phone, or anyother type of computing device suitable for practicing one or moreembodiments of the present disclosure. In operation, computing device1300 is configured to execute instructions associated with an edgemeasurement algorithm 1390, computer-implemented process 800,computer-implemented process 1200, and/or a treatment planning system1311, as described herein. It is noted that the computing devicedescribed herein is illustrative and that any other technically feasibleconfigurations fall within the scope of the present disclosure.

As shown, computing device 1300 includes, without limitation, aninterconnect (bus) 1340 that connects a processing unit 1350, aninput/output (I/O) device interface 1360 coupled to input/output (I/O)devices 1380, memory 1310, a storage 1330, and a network interface 1370.Processing unit 1350 may be any suitable processor implemented as acentral processing unit (CPU), a graphics processing unit (GPU), anapplication-specific integrated circuit (ASIC), a field programmablegate array (FPGA), any other type of processing unit, or a combinationof different processing units, such as a CPU configured to operate inconjunction with a GPU or digital signal processor (DSP). In general,processing unit 1350 may be any technically feasible hardware unitcapable of processing data and/or executing software applications,including edge measurement algorithm 1390, computer-implemented process800, computer-implemented process 1200, and/or treatment planning system1311.

I/O devices 1380 may include devices capable of providing input, such asa keyboard, a mouse, a touch-sensitive screen, and so forth, as well asdevices capable of providing output, such as a display device and thelike. Additionally, I/O devices 1380 may include devices capable of bothreceiving input and providing output, such as a touchscreen, a universalserial bus (USB) port, and so forth. I/O devices 1380 may be configuredto receive various types of input from an end-user of computing device1300, and to also provide various types of output to the end-user ofcomputing device 1300, such as displayed digital images or digitalvideos. In some embodiments, one or more of I/O devices 1380 areconfigured to couple computing device 1300 to a network.

Memory 1310 may include a random access memory (RAM) module, a flashmemory unit, or any other type of memory unit or combination thereof.Processing unit 1350, I/O device interface 1360, and network interface1370 are configured to read data from and write data to memory 1310.Memory 1310 includes various software programs that can be executed byprocessor 1350 and application data associated with said softwareprograms, including edge measurement algorithm 1390,computer-implemented process 800, computer-implemented process 1200,and/or treatment planning system 1311.

FIG. 14 is a block diagram of an illustrative embodiment of a computerprogram product 1400 for implementing a method for segmenting an image,according to one or more embodiments of the present disclosure. Computerprogram product 1400 may include a signal bearing medium 1404. Signalbearing medium 1404 may include one or more sets of executableinstructions 1402 that, when executed by, for example, a processor of acomputing device, may provide at least the functionality described abovewith respect to FIGS. 1-13 .

In some implementations, signal bearing medium 1404 may encompass anon-transitory computer readable medium 1408, such as, but not limitedto, a hard disk drive, a Compact Disc (CD), a Digital Video Disk (DVD),a digital tape, memory, etc. In some implementations, signal bearingmedium 1404 may encompass a recordable medium 1410, such as, but notlimited to, memory, read/write (R/W) CDs, R/W DVDs, etc. In someimplementations, signal bearing medium 1404 may encompass acommunications medium 1406, such as, but not limited to, a digitaland/or an analog communication medium (e.g., a fiber optic cable, awaveguide, a wired communications link, a wireless communication link,etc.). Computer program product 1400 may be recorded on non-transitorycomputer readable medium 1408 or another similar recordable medium 1410.

In sum, embodiments described herein provide techniques for controllingthe size, shape, and/or power intensity distribution of a beam spot in aradiation therapy system. The herein-described techniques facilitatetuning of the beam spot to improve consistency between the attributes ofthe beam spot and pre-configured beam data that is included in atreatment planning model. As a result, performance of an X-ray beamgenerated by the beam spot closely matches the performance assumed forthe X-ray beam in the treatment planning system.

The descriptions of the various embodiments have been presented forpurposes of illustration, but are not intended to be exhaustive orlimited to the embodiments disclosed. Many modifications and variationswill be apparent to those of ordinary skill in the art without departingfrom the scope and spirit of the described embodiments.

Aspects of the present embodiments may be embodied as a system, methodor computer program product. Accordingly, aspects of the presentdisclosure may take the form of an entirely hardware embodiment, anentirely software embodiment (including firmware, resident software,micro-code, etc.) or an embodiment combining software and hardwareaspects that may all generally be referred to herein as a “circuit,”“module” or “system.” Furthermore, aspects of the present disclosure maytake the form of a computer program product embodied in one or morecomputer readable medium(s) having computer readable program codeembodied thereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readable signalmedium or a computer readable storage medium. A computer readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, or device, or any suitable combination of the foregoing. Morespecific examples (a non-exhaustive list) of the computer readablestorage medium would include the following: an electrical connectionhaving one or more wires, a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), an optical fiber,a portable compact disc read-only memory (CD-ROM), an optical storagedevice, a magnetic storage device, or any suitable combination of theforegoing. In the context of this document, a computer readable storagemedium may be any tangible medium that can contain, or store a programfor use by or in connection with an instruction execution system,apparatus, or device.

While various aspects and embodiments have been disclosed herein, otheraspects and embodiments will be apparent to those skilled in the art.The various aspects and embodiments disclosed herein are for purposes ofillustration and are not intended to be limiting, with the true scopeand spirit being indicated by the following claims.

We claim:
 1. A computer-implemented method for tuning a beam spot in aradiation therapy system, the method comprising: configuring an electronbeam to generate a first beam spot on an electron-beam target of theradiation therapy system; generating, using an imager of the radiationtherapy system, a first plurality of projection images of the first beamspot, wherein each of the projection images of the first beam spot isgenerated with a line of sight blocked between the imager and adifferent respective portion of the beam spot by a portion of acollimator of the radiation therapy system; based on the first pluralityof projection images, determining a value for one or more beam spotquality metrics associated with the first beam spot; and based on thevalue, determining whether the first beam spot is outside a specifiedquality range.
 2. The computer-implemented method of claim 1, furthercomprising, in response to determining that the first beam spot isoutside the specified quality range, modifying at least one parameter ofan electron-beam-generating component of the system to a new value. 3.The computer-implemented method of claim 2, wherein modifying theparameter of the electron-beam-shaping component of the system compriseschanging a magnitude of a first solenoid current to the new value. 4.The computer-implemented method of claim 1, further comprising, whilethe imager generates the first plurality of projection images of thefirst beam spot, for each respective projection image, positioning theportion of the collimator at a different respective rotational angleabout a rotation axis of the collimator.
 5. The computer-implementedmethod of claim 1, wherein shaping the first X-ray beam that originatesfrom the first beam spot using the portion of the collimator comprisesparking the portion of the collimator in a fixed position relative to arotation axis of the collimator.
 6. The computer-implemented method ofclaim 1, wherein the one or more beam spot quality metrics include oneor more of a beam spot area, a beam spot elongation, a beam spot powerper unit area, or a beam spot center point offset from an ideal centerpoint location.
 7. The computer-implemented method of claim 1, furthercomprising, measuring a dose rate of an X-ray beam that originates fromthe first beam spot.
 8. The computer-implemented method of claim 1,wherein determining the value for one or more beam spot quality metricsassociated with the first beam spot comprises generating atwo-dimensional intensity distribution of the first beam spot.
 9. Aradiation therapy system, the system comprising: an imager; atreatment-delivering radiation source that includes an electron-beamtarget and is configured to direct a treatment beam to a target volumeof patient anatomy; and one or more processors configured to: configurean electron beam to generate a first beam spot on the electron-beamtarget; generate, using the imager, a first plurality of projectionimages of the first beam spot, wherein each of the projection images ofthe first beam spot is generated with a line of sight blocked betweenthe imager and a different respective portion of the beam spot by aportion of a collimator of the radiation therapy system; based on thefirst plurality of projection images, determine a value for one or morebeam spot quality metrics associated with the first beam spot; and basedon the value, determine whether the first beam spot is outside aspecified quality range.
 10. The computer-implemented method of claim 9,wherein generating the two-dimensional intensity distribution of thefirst beam spot comprises reconstructing the two-dimensional intensitydistribution using an edge measurement algorithm.
 11. The system ofclaim 9, wherein the one or more processors are further configured to,in response to determining that the first beam spot is outside thespecified quality range, modify at least one parameter of anelectron-beam-generating component of the system to a new value.
 12. Thesystem of claim 11, wherein the one or more processors are furtherconfigured to, after modifying the at least one parameter of theelectron-beam-shaping component of the system to the new value:configure the electron beam to generate a second beam spot on theelectron-beam target of the radiation therapy system with the electronbeam using the new value of the parameter; generate, using the imager, asecond plurality of projection images of the second beam spot, whereineach of the projection images of the second beam spot is generated witha line of sight blocked between the imager and a different respectiveportion of the beam spot; and based on the second plurality ofprojection images, determine a value for the one or more beam spotquality metrics associated with the second beam spot.
 13. The system ofclaim 11, wherein modifying the parameter of the electron-beam-shapingcomponent of the system comprises changing a magnitude of a firstsolenoid current to the new value.
 14. The system of claim 13, whereinmodifying the parameter of the electron-beam-shaping component of thesystem further comprises changing a magnitude of a second solenoidcurrent.
 15. The system of claim 9, wherein the one or more processorsare further configured to shape a first X-ray beam that originates fromthe first beam spot using a portion of a collimator of the radiationtherapy system while the image generates the first plurality ofprojection images.
 16. The system of claim 15, wherein the one or moreprocessors are further configured to, while the imager generates thefirst plurality of projection images of the first beam spot, for eachrespective projection image, position the portion of the collimator at adifferent respective rotational angle about a rotation axis of thecollimator.
 17. The system of claim 9, wherein the one or moreprocessors are further configured to, in response to determining thatthe first beam spot is within the specified quality range: configure theelectron beam to generate the first beam spot on the electron-beamtarget of the radiation therapy system; determine a value for one ormore radiation field quality metrics for a first X-ray beam thatoriginates from the first beam spot; and based on the value for the oneor more radiation field quality metrics, determining whether the firstX-ray beam is outside a specified radiation field quality range.
 18. Thesystem of claim 9, wherein modifying the parameter of theelectron-beam-shaping component of the system comprises changing adirectionality of a first solenoid current.
 19. The system of claim 18,wherein modifying the parameter of the electron-beam-shaping componentof the system further comprises changing a directionality of a secondsolenoid current.
 20. A method of improving consistency between one ormore attributes of a beam spot in a radiation therapy system andpre-configured beam data included in a treatment planning model of theradiation therapy system, the method comprising: measuring the one ormore attributes of a first beam spot based on a plurality of projectionimages of the first beam spot, wherein each of the projection images ofthe first beam spot is generated with a line of sight blocked between animager of the radiation therapy system and a different respectiveportion of the beam spot by a portion of a collimator of the radiationtherapy system; determining a value for one or more radiation fieldquality metrics for a radiation beam that originates from the first beamspot; based on at least one of the one or more attributes of the firstbeam spot and the value for the one or more radiation field qualitymetrics for the radiation beam, modifying a parameter of anelectron-beam-generating component of the radiation therapy system froma first value to a second value; and generating a second beam spot withthe electron-beam-generating component of the radiation therapy systemusing the second value, wherein one or more attributes of the secondbeam spot are closer in value to the pre-configured beam data than theone or more attributes of the first beam spot.